13,595 reputation
13478
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location Stockholm, Sweden
age 28
visits member for 4 years, 10 months
seen 18 hours ago

I am interested in the moduli space of curves and also other things. I am currently on parental leave.


3h
awarded  Revival
Sep
10
comment When are induction and coinduction of representations of Lie groups isomorphic? When they are compact? Semisimple?
@Sasha You may very well be right, but I don't understand why my argument doesn't cut it. Why do you need the condition on the relative canonical class?
Sep
10
answered When are induction and coinduction of representations of Lie groups isomorphic? When they are compact? Semisimple?
Sep
5
comment $\ell$-adic monodromy theorems (over $\mathbb{C}$)
For Q1 I guess you meant to assume that y is in V. I believe the answer is no in general. I guess you know that it's true if V=Y so you're in the situation of the usual invariant cycle theorem.
Sep
4
comment Feynman integrals in algebraic geometry
@user125763 I'm flattered, but I don't think I have much useful to say about this circle of ideas. (And the question is in any case closed!)
Sep
3
comment Feynman integrals in algebraic geometry
You should look at the book "Feynman motives" by Marcolli.
Aug
31
comment Finite subgroups of mapping class groups
"I vaguely recall hearing that Mod(Σ) has no faithful, finite dimensional linear representations." --- Actually, it's a major open problem whether or not mapping class groups are linear.
Aug
27
comment What are TQFTs that are multiplicative under connected sums? Do bordisms with connected sum as monoidal product exist?
@Turion I think მამუკა ჯიბლაძე has answered your question already, but I think it's worth commenting that connected sum is not a bifunctor. Indeed $M \# N$ depends on the choice of a ball in $M$ and in $N$, so it's only well defined up to a noncanonical isomorphism.
Aug
25
comment symmetric theta structures and arithmetic subgroups
What's the question?
Aug
23
comment An algorithm and symbolic manipulation for IF-THEN-ELSE
I was indeed tacitly assuming that every IF should be followed by a boolean expression and a THEN, and conversely, that every THEN should be preceded by a boolean and an IF.
Aug
23
answered An algorithm and symbolic manipulation for IF-THEN-ELSE
Aug
21
awarded  Enlightened
Aug
21
revised Is there a higher Grothendieck ring?
added 165 characters in body
Aug
21
awarded  Nice Answer
Aug
21
revised Is there a higher Grothendieck ring?
added 3933 characters in body
Aug
21
answered Is there a higher Grothendieck ring?
Aug
18
comment Constructing a space with prescribed cohomology ring
@Fedotov Look again at Theorem 1.2 of the Andersen-Grodal paper. There is for instance no topological space with mod 5 cohomology ring $\mathbf F_5[x]$, $\vert x \vert = 6$. Your argument seems to hinge on the following lemma, which is false: if $A$ and $B$ are (graded) $\mathbf F_p$-algebras which become isomorphic when tensored with $\overline{\mathbf F}_p$, then $A$ and $B$ are isomorphic already as $\mathbf F_p$-algebras.
Aug
18
comment A group allowing exactly 7 group topologies
@VivekShende If $G$ is infinite, then $G \times G \to G$ is not continuous for the cofinite topology.
Aug
18
comment Constructing a space with prescribed cohomology ring
@Fedotov Did you look at the paper I mentioned? Your claim contradicts for instance the results of ams.org/mathscinet-getitem?mr=1670237 . I don't see why the isomorphism $S \otimes_{\mathbf F_p} \overline{\mathbf F}_p \cong H^\bullet(X,\mathbf F_p) \otimes_{\mathbf F_p} \overline{\mathbf F}_p$ should be Frobenius-equivariant.
Aug
16
comment Constructing a space with prescribed cohomology ring
@Fedotov This answer is wrong. It is not true that any $\mathbf F_p$-algebra occurs as the mod p cohomology of a space. Look at the introduction to the paper that Matthias Wendt linked to, and the references there.